What would you need to expand the simple 10/100BaseT Ethernet adding a network of lets say 4 additional computers.It not that difficult, all you need to install a NIC card the appropriate driver software into each additional PC, and connect them up via a multi-port 10BaseT or 100BaseT hub. We'll look closerat these shortly,but for the moment just think of hub as a kind of data distribution box which sends beefed-up copies any data packets arriving at any other or to all of the other ports (NIC cards) in the network.

The general arrangement of this kind of the hub-based network is shown in the FIG below, you can see the network now has a physical "STAR" topology. Each of the PCs are connected to a port on the hub, an equal point in the network or a "PEER" in the network.

The length of each cable should be kept less than 100 metres,(325 feet) and the maximum distance between any device on the network is less than 200 metres (650 feet). The other requirment is that all UTP cabling be rated for catagory 5, specifically for 100BaseT networks.NETWORK INTERFACE CARD (NIC)

Typically all PCs currently include a NIC or interface card on the motherboard, order device will require a NIC card and drivers to be installed BEFORE being attached to the network.
for a Ethernet network to ber propertly configured. This NIC interface includeds the devices hardwired MAC address. Each MAC address is different for EVERY Device.

Finally, there is a single RJ-45 socket on the NIC card or motherboard's ethernet interface. This interface will provide a couple of LED lights to provide a visual indications of the networks activity at either 10BaseT or 100BaseT throughput rates.

UTILIZING HUBS IN CASCADE

As we've seen the simplest way to hookup more-than two pes in a network is using a hub. Hubs are relatively simple and low in cost, and they're essentially multi-port repeaters or signal boosting amplifiers. They have no built-in 'intelligence'; any packet of network data which arrives via the input connections of the hub's port is simply amplified and sent out again via all the output ports, which would include the port it arrived from.Cost effective Ethernet hubs are available with up to eight ports, this means that the simplest hub-based or star network scheme can be configured to utilize as many as eight (8) link up computers and/or applicances to a common network.

The simplity of a Ethernet hub based network is that is is easy to add additional devices to the network simply by cascasding an additonal hub off of one of the ports of the orginating hub, in place of one of devices orginally connected.
Beaware there is a opertionally important point when cascadnig Hubs For the cascading to function correctly, there must be a "cross-over" connection between the cascaded hubs. In other words, the input connection of the orginating hub must connect to the output connection of the other. This arrangement actually creates a "daisy chain" configuration of the connected hubs, while allowing the ports of the total hubs to be in a increased hub network.Many hubs are designed so one of their portscan have these connections flipped over within the hub itself via an internal DIP switch. This allows that port to be configured as the "UPLINK" port to the cascaded Hubs.If you do not have a hub with a port which can be switched configured for upllnking, you simply use thls hub as the cascaded or "expansion" hub and link the two (2) hubs together using a normal straight-through Cat 5 patch cable.
Now if either hub can be re-configured to have an uplink port. This is simply configured with a cross-over cable utilizing the exisiting normal port's configuration. In this case the required transmit and receive leads are provided by the cross-over leads within the special cable.

HUBS IN CASCADE con't

By the way, the same rules apply to cascading switches. The UTP connecting cables should be no longer than 5 metres (16 feet) when used to connect cascaded hubs or switches. This reduces the networks propagation delays to be within the specifcations of both 10BaseT and 100BaseT providing for reliable network operations.SWITCHES COMPARED TO HUBS

It is possible to continue to expand your Ethernet network by cascading hubs, but after a point you will notice the the network throughput is slowing down. This slowdown is being casued by network "congestion" This slow down in speed is caused by the cascading of "DUMB" hubs. As described earlier hubs just boost or amplify and the data presented at any of its ports and re-transmit the data from all of the ports again.
Problem.... In a network linked with various hubs, every PC, network appliance, and NIC card receives ALL the data packets broadcast of the cascaded hum configured network. Every data packet on the network must be evaluated by each device, i.e; NIC, PC or appliance choicing to accept the packet or ignore it. This makes the network a huge "party line" and no one device to direct and route the huge amount of data presented to every network device. This congestion causes the network to slow down.
This concern is easily solved or minimized by replacing dumb hubs with smart switches. Switches' look very similar to hubs, but they're the step above in terms of intelligence. As discussed earlier hubs just boost and route data packets for broadcast to every port. A switch checks the source and destination fields in each of the data packet's frames to relize where the packet orginated and where it is being sent. Switches have internal memory where it stores: the hardwired network address of each NIC that is currently connected to its ports, or NIC addresses of other devices connected sowhere else in the network. Eash switch has a matrix switch array with eletronically addressed switches that can direct any incoming data frame to the output pair of which is cinnected ti the addresses NIC or device.
A switch's operation is much improved in intelligence over a simple dumb hub. Like an air traffic controller the switch routes the data packets to the "address" or NIC is has been programmed to route, as a result the network's speed is not compromised by massive undirected congestion network traffic. The network can now process the data packets with nearly full speed.MIXING HUBS AND SWITCHES

A network can contain both hubs and switches. The top level hub should be relaced by a switch will show great improvements in the networks overall operation. Then at lower level tiers can utilize hubs. This arrangement can show to be very cost effective since switches are 50% more in cost than similiar ported hubs. Replacing lower level hubs with switches will increase the network's speed but can not be justified due to the additional expense.

It's important to note that if a switch is used at the networks top level and the network includes a PC shared as the complete network's resource for all other devices linked to the network, i.e; print servers, hard disk storage or RAID devices. The primary PC should be linked to a port on the top level switch. This will insure that the network throughput is not compromised by routing massive data packets though dumb hubs.

The choice to confirgure the network with switches and/or hubs is greatly up to the networks designer's needs of speed vs. cost.